A mycorrhizal fungus is a soil symbiotic micro-organism that infects to roots of a plant, obtains photosynthetic products from the plant, and in return for this, contributes to the supply of nourishing water and the impartation of environmental stress tolerance and disease and pest resistance to the plant. Among mycorrhizal fungi, especially arbuscular mycorrhizal fungi (AMF) can create a symbiotic relationship with practically all terrestrial plants. By developing effective use methods of these fungi with their functions and roles in mind, these fungi can, hence, reduce the use amounts of chemical fertilizers and chemically-synthesized agrochemicals or can make them no longer needed. They are, accordingly, expected to enable an increase in the production of safe, secure and sustainable foods.
It has recently come clear that partner bacteria, which grow in and around spores of AMF, promote the hyphal growth of AMF and have phosphate solubilizing ability, nitrogen fixing ability and antagonistic action against plant pathogens (see, for example, Non-patent Documents 1 and 2).
As a result of a study on the introduction of bahiagrass, one of partner plants in the hydroponic cultivation of salad lettuce, and AMF, it has been found that the introduction of bahiagrass gives no adverse effect on the growth of salad lettuce or tends to slightly retard its growth and that the use of AMF reduces nutrient competition between salad lettuce and bahiagrass when such nutrient competition tends to take place under stress such low temperatures (see, for example, Non-patent Document 3).